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How does maintenance differ for military fighters/bombers vs. commercial airliners?
And why do military fighters/bomber require so many maintenance hours compared to commercial airlines, which seems like just kicking the tires? What do they actually do?
How does maintenance differ for fighters vs. bombers?
As many of the comments and answers have illuminated, "different missions drive different design priorities." Examples of differences in specific maintenance activities would be greatly appreciated.

Based on the inspection/maintenance schedule Johnny listed in this answer, I wouldn't say commercial airlines just 'kick the tires'.

@FreeMan I meant that in the [uninformed] stereotype, airliners only perform maintenance once every 100-600 hours, whereas fighters are maintained after every flight. But mostly, it was for levity. - Thanks for the link, btw. I was going to ask this question yesterday, so I didn't notice the new question/answer.

@FreeMan A D-check is when they strip down and rebuild the aircraft, isn't it?

At an estimated 50,000 hours to perform it, that is entirely likely, however, I'm not the expert.

Standard military adage, "If its not leaking, its empty".  I wouldn't assume that military aircraft have superior reliability and maintenance because they receive more frequent attention.  This is likely just a side effect of flying in a more stressful flight regime than typical civilian aircraft.  Constantly bending the jet takes a toll on the aircraft.

Military aircraft are high performance machines that operate far beyond the performance envelope of commercial passenger aircraft. As a civilian analogy,  F1 race car gets its engine rebuilt every 500 miles or so, while a commercial bus might go 15,000 miles between oil changes (or longer if they have an oil analysis program) and with proper maintenance, can stay on the road for 500,000 miles or more without needing a major engine overhaul.

@Johnny So do they perform the same maintenance activities, just on an accelerated schedule?

I don't know anything about Military aircraft maintenance, I'm sure there are a lot of similarities between military and commercial aircraft maintenance, but also some very significant difference (like weapons systems), just like there's similaries between F1 race car maintenance and commercial bus maintenance (like the KERS system on a race car but not on many buses, and an air braking system on a bus that's not on a race car)

whereas fighters are maintained after every flight  The routine after flight service is not that different to a commercial aircraft.  Check fluids, check gases, kick the tyres etc etc.  However, most servicing includes rectification since the aircraft a) operates in much hasher regimes b) contains consumable stores that are either not present on commercial aircraft or are rarely used c) use avionics and other delicate kit which is half a generation behind commercial kit (in the main).

To give you an analogy.  An Airbus 330 used for troop transport in a military role will have a very similar maintenance schedule to a similar commercial aircraft.  The primary responsibility for the schedules lies with the manufacturer, then the certifying body and finally the "engineering authority" of the military arm operating the aircraft.

To some extent you could compare with the Concorde sub sonic aircraft.(excluding the ammunations,missiles,heavy payloads)

The F1 vs Bus analogy is a good one. perhaps a Rally car would be better since F1's are practically rebuilt after each race.
Civilian airliners are designed for long service cycles. When a new airliner is proposed a large part of the design brief will be about making it as efficient as possible to operate which means it must spend as much time as possible in the air making money for its owner.
Military aircraft are designed around performance and mission requirements instead of efficiency. The cost of more frequent maintenence is off-set by their in-mission performance.

let's not forget the CYA approach to risk management employed by the military.  i can tell you the aircraft i've worked on (not fighters per se, but military aircraft nonetheless) have required regular hourly-and cycle-based maintenance (12-hour, 25-hour, 50-hour, 1000 landings, etc.) as well as pre-/post-/thru-flight inspections, and finally periodic calendar-based inspections.

Upvoted @SHAF "I wouldn't assume military...have superior reliability." Spot on. My experience Air Natl. Guard and active duty. Required/routine mx was the same. Active duty planes flew more hours but broke more often far beyond the rate of hours. Natl Guard folks tend to be older and vastly more experienced and it showed dramatically in mx. On active duty I shut down 6 engines in about 1st 100 hrs, 3 were on consecutive flights. But in the Guard maybe 3 total in 1,200 hrs - and at least 10 yr older planes.

I think a few things need to be examined here:
1) The type of flying.  A commercial aircraft is closer to a military C-17 than a B-52 or F-16 in how it is used.  It has several stops throughout the day for loading and unloading.  The maintenance in between stops does not need to be very extensive - because it has just landed, presumably working fine, the things that need to be checked primarily involve what has the most chance of decaying during a flight (tires, oil, general wear and tear, etc).  Fighters/bombers don't generally fly several legs in a day.  Fighters might double/triple turn, and in between each of these flights the maintenance inspection is a much lower requirement than between each day of flying.
2) Component Requirements.  Supersonic jet engines need maintenance more often than high bypass commercial engines.  They are stressed much more, and work on a much tighter margin of error, thus fighter/bomber aircraft need maintenance more often.
3) Age.  Military fighter/bomber aircraft are on average much older than the average commercial aircraft.  B-52's are from the 50's, and B-1's are from the 80's (along with most of the fighter fleet).  Older aircraft require more maintenance, and there is no avoiding it.
Between fighters and bombers, they each have different flying styles.  Fighter engines work a lot harder than bomber engines (except the B-1, which essentially has the same engine as an F-16), and thus require maintenance more often.  Bombers are much larger, and have more systems that can break.
Hope this helps.
Update: Incorporating a suggestion from the comments below, it is probably useful to specifically mention a few more specific maintenance items unique to combat aircraft
1) Ejection Seats:  Most military combat aircraft carry ejection seats, which have a very specific maintenance routine.  This may include repacking the associated parachute, and checking to ensure that all components are functional/in good repair.
2) Weapons:  The obvious difference between fighters/bombers and commercial airliners is that they carry weapons.  This means that there is a software package that needs to be maintained (that controls the weapons), the aircraft hardware needs to be maintained (ie bomb bays, missile racks, hard points, etc), and the weapon itself requires building/deconstruction.
3) Flight Computer:  Combat aircraft often have tactically specific functions in their flight computer that a commercial airliner would not.  There are routines to help calculate bomb trajectory, to link with other combat aircraft and many other military specific tasks that a commercial airliner would not need.
I would agree with an earlier statement stating that performance has a slightly higher emphasis than reliability in military aircraft than in commercial aircraft.  It's easy to see how the requirement to carry bombs/missiles increases aircraft gross weight, which lowers fuel efficiency.  Every internal bomb bay could potentially be a fuel tank extending range.  Hard points, even when bombs aren't installed, cause drag lowering performance.  In the end, designers have to determine which capability is more important - endurance, payload, power, etc.  You may want to install a triply redundant INS in a fighter aircraft, but you're adding weight that decreases performance, and taking space which could be devoted to other avionics (like radar).

Do you have any examples of specific maintenance activities unique to fighters/bombers (vs airliners)?

The biggest thing to point out is that fighters/bombers have weapons, and weapons systems which need maintenance. So the hard points, weapons delivery systems, etc all need maintenance while commercial aircraft do not.  Fighter/bombers also have ejection seats, where commercial aircraft do not.  These seats require regular maintenance (parachute repacks, inspections, etc).

Interesting. How do you actually maintain a weapon? What something specific you actually do?

@tmptplayer That is a good point to add to your answer. You might also mention the design tradeoffs involved with the different requirements.

@HephaestusAetnaean When you eject a bomb, an electric charge detonates a small explosive cartridge (roughly the size of a shotgun shell) which actually moves the mechanism holding the bomb.  Naturally, anything which has to endure explosive charges (even small ones) will require inspection, cleaning and, occasionally, replacement.  Additionally, modern aircraft guns are usually multi-barrel (Gatling guns).  Any gun is going to have lots of small, intricate parts for chambering, firing and ejecting the rounds, plus moving rounds from the magazine (chain mechanisms, not WW II-era belts).

@fooot  - answer modified per your suggestion.  I'm not entirely positive on the root of the question, so hopefully these considerations are what you're after.

Military aircraft are designed to maximize performance, while commercial airliners are designed to maximize reliability.
That's not to say that reliability is unimportant for the military aircraft or that performance is unimportant for the airliners, but when almost everything is done and the last tradeoff is considered, the military jet can accept a little more maintenance in return for a little better performance, while the airliner will probably sell better with better reliability & the ability to go longer between maintenance down-time, even at the cost of the last 0.2% better performance/weight/economy/etc.
The assumption for military aircraft, fighters & bombers in particular, is that they'll finish the day back at their base, and they CAN be worked on for several hours before they're launched again.  (Generality here -- yes higher tempo ops are possible, but it's the exception not the rule.)  Airliners, on the other hand, typically will fly for days between maintenance checks (beyond adding oil, checking tire pressure, and maybe swapping a particular broke part) -- and that's what's desirable because that's how the airplane makes the most money.  So that ability to go for so long between maintenance checks is built in because that's what the customer (the airlines) demands.
Could you get more performance out of an airliner if you were willing to accept more maintenance costs?  Sure, but it wouldn't be worth it to the airlines.  At the extreme, the Concorde, for all its cool factor, was an economic disaster, even though its performance was superlative.
The military aircraft have redundant systems in order to survive -- limp back to base.  Commercial aircraft have redundant systems in order to be able to be dispatched again -- stay in service until repairs can be performed.  (Obviously, not everything can be deferred; some things ground the airplane & have to be fixed before it flies again... but a LOT of stuff in the airliner can be deferred & you still have redundant capability to land safety even if another system goes down.)  As an example, the F-16 was (may still be) single-INS + single-FMS.  The system works or you don't launch.  Modern airliners have two or three INS's and FMC's -- dispatch with one INS inop is possible (probably day VMC only), and dispatch with one FMC inop has minimal limitations (no long overwater legs, essentially).
Different missions drive different design priorities, and that in turn shows up as differing levels of maintenance that's required.

Yes, I'm familiar with the different design priorities. Hmm, I think i should reword to question to emphasis the specific activities. Thanks for the INS/FMS example. And thanks for answering!

fwiw, us army readiness goals are 75% fmc (fully mission capable), 80% mc (one or more design capabilities/requirements cannot be met), with no more than 10% downtime due to parts not on hand, no more than 10% downtime due to maintenance, and no more than 5% time spent "partially mission capable".  source: ar 700-138


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What are "Alternate Minimums"?
As I asked question about weather minimums yesterday, I've read some material including TERPs. And In the FAA 8260.3b, 'Taking and Landing Minimims' 3.1 there is one sentence "alternate minimims, when specified, must be stated as ceiling and visibility."
But I don't know What alternate minimums exactly means because I am not native English speaker. I have used English dictionary to find exact meaning but failed.
What is the difference between approach minimums and alternate minimums?

FAR 91.169 states that IFR flight plans must include an alternate airport unless the weather is at least 2000 ft ceiling and 3 miles visibility, from one hour before to one hour afterwards (1-2-3 rule).
The same regulation also states that the alternate airport must meet the following critera:

(c) IFR alternate airport weather minima. Unless otherwise authorized
  by the Administrator, no person may include an alternate airport in an
  IFR flight plan unless appropriate weather reports or weather
  forecasts, or a combination of them, indicate that, at the estimated
  time of arrival at the alternate airport, the ceiling and visibility
  at that airport will be at or above the following weather minima:

(1) If an instrument approach procedure has been published in part 97
    of this chapter, or a special instrument approach procedure has been
    issued by the Administrator to the operator, for that airport, the
    following minima:

(i) For aircraft other than helicopters: The
      alternate airport minima specified in that procedure, or if none are
      specified the following standard approach minima:
(A) For a precision approach procedure. Ceiling 600 feet and visibility 2 statute miles.
(B) For a non-precision approach procedure. Ceiling 800 feet and visibility 2 statute miles.

So, Do you mean that 'alternate minimums' means alternative aiport's minimum? If yes, Does the word 'alternate' imply 'alternative airport'?

Yes the forecast weather for the alternate airport must be above minimums.

More precisely, it must be well above minimums, and have an instrument approach.

It doesn't have to be well above anything except what's written above. There are plenty of approaches that are 800/2. And since the alternate minimums are below basic VFR of course it has to have an instrument approach.

Also, some procedures aren't eligible for use as an alternate approach.

That would make an excellent answer to a question about selection an approach at an alternate

...And some approaches have non-standard minimums for their use as an alternate.  It is also possible for an airport with no instrument approach to be used, provided forecast weather allows for descent from the MEA to the airport under basic VFR.

The difference between APPROACH minimums, and ALTERNATE minimums:
APPROACH minimums are stated on each approach plate, for instance, 200 ft. ceiling with 3 mi.  visibility.  It's a real-time minimum, because it only affects whether or not you can begin that particular instrument approach.  On arrival, you check the airport's weather (METAR, for instance) and if the real weather is reported better than the required weather for a particular approach, then you can begin that approach.  Therefore, you need to take the destination weather forecast into account when planning.
ALTERNATE minimums affect your PLAN, even BEFORE you take off, and is not related to approach minimums.  An "alternate" refers to a second airport you identify in your planning that you can go to if the weather at the destination turns too bad to land.  The thinking is that, if the weather at the destination is FORECASTED to be good around your arrival time (an hour before til an hour after), then you shouldn't need to list an alternate airport in your flight plan.  Generally, the destination's weather has to be FORECASTED more than 2,000 ft. ceilings and 3 miles visibility, or if not, you have to IDENTIFY an alternate destination airport in your flight plan.  The FORECASTED weather at the ALTERNATE airport has to be better than a certain ceiling / visibility, too.  You have to look at the approaches available at the alternate to know what the minimum requirements are there.  If the alternate airport has a "precision" approach (for instance, an ILS), the FORECASTED weather at the ALTERNATE has to be at least 600 ft. ceiling and at least 2 mi visibility, otherwise you can't list it as an alternate.  But airports with a non-precision approach (for example, a VOR-A approach) require better  conditions with 800 ft. ceilings.

I found an excellent article about it at IFR Magazine.
Basically, to qualify as an alternate airport, the alternate must have certain forecast weather conditions (600-2 for precision approach, 800-2 for non-precision.) These are the "alternate minimums".
However, those are just the default values. Many airports have different values, in which case the alternate minimums will be published on the approach plate (example: PAO VOR approach, top-left, next to the inverted 'A')

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Can these vortices be dangerous?
There is a question related to this one right here but I'm more interested in the danger of those vortices. Are they very dangerous to cause a wake turbulence for the aircraft that  comes behind this? Can it cause an accident or so?

Source

Are you referring to the pattern produced by the propellers?

Yes. The white ones that come out of the engine

The wake vortices of the wing are more significant so the effects of these vortices are probably masked.

@kepler22b, remember, that the vortices are always there. They are just not always visible.

No.
The wing does a great job in straightening the propeller swirl, but adds its own vortex. Wake turbulence is dominated by the flow field around the wing.

While @Peter Kämpf 's answer is great and sufficient to answer the question, I would like to add a clarification (which should be a posted as a comment, but is too long for this format).
In the image in the question, there are visible streams of condensed water vapor from the atmosphere. These streams are only present at the blade tips. The question seems to assume that these streams depict the wake from the propellers. They don't, or more accurately there are only a very small part of the wake volume.

1. Images of tip vortices from different devices
1a, tip vortex from a propeller

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Condensed water forms because the change of pressure is adiabatic, in simple terms it occurs with little exchange of heat with the neighboring regions. It occurs first where the pressure difference is large and the transition quick. (By the way, note the 8 rockets used to assist for takeoff.)
1b, tip vortex from a wing

Source
1c: tip vortex from a rotor

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There is not doubt the rotors spin in opposite direction.
1d, tip vortex from a wind turbine

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Notice: Actually after looking at oddities on this image (the direction of the wind), I realized that this is an experimental turbine used by the US DoE and the NREL to study winds. The white stream is actually smoke released from the blade. Probes are visible on the leading edge to measure speed at different locations of the blade. I keep the image as it's a good one.

2. Full wake turbulence
Contrary to the previous images, the ones below show the whole turbulence created by the same airfoils. While the tip vortices are materialized by condensed water vapor created by a transition from high to low pressure at the tip of the devices, the whole wake is visible only if air is not clear.
2a, turbulence from a propeller

Source
Principle (no photo found, do you have one?)
2b, turbulence from a wing

Source
2c: turbulence from a rotor

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2d, turbulence from a wind turbine

Source

3. Images where both effects are combined
Note that regardless of whether they are visible or not, both the tip vortices and full wake always exist. Their visibility greatly depends, like contrails, on the air moisture and temperature.
As explained by @Peter, the energy of the tip vortices is diluted in the energy of the actual wake turbulence:

Source

Source: What causes a plane's wing tips to leave a small white vapor trail?

4. Complexity of the wake
Wake from a wind turbine, mixing all sources of turbulence:

Source

The tip vortex is initially a very small part of the wake, created by the high pressure air escaping from the low side of the wing. The whole wake volume grows in length and diameter as the airfoil moves. The vertex diameter grows, until there is no more energy left and air stops moving (see images in §3):

Source

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See this question for details: How does an aircraft form wake turbulence?

And let me tell you, if you fly behind a wind farm you know those turbines do produce wake turbulence!

And my I say, incredible answer! Well done!

Some very nice wallpapers there

+1, especially for the pictures. But... the last....  I'm sure you caught them spraying...

I disagre with " should be a posted as a comment" as "there are only a very small part of the wake volume" is an answer (and you provide good clarifications and illustrations to Peter's answer)

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What are these markings on the A380 wing?
There are some "markings" over the wings and the horizontal stabilizer. Could somebody explain what they are?

Note, these markings are not restricted to the A380. Almost all commercial aircraft in similar shape have these markings on their flight control surfaces.

The darker areas denote where it is safe to step. Stepping outside of these areas could cause damage to the aircraft.
Here's a closeup of the warning:

(This happens to be a photo of Qantas Flight 32 after its un-contained engine failure)

Why walking is required on the wing?

New bottom-tier Ryanair ticket. In all seriousness, maintenance personnel are the most likely people to have to heed this warning.

So the warning is printed both ways so it can be read by those already walking outside the allowed area?

.. or someone on a step ladder, about to step onto the area


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Could a civilian aircraft in distress land in Area 51?
Just curiosity, but in case of a real life-threatening emergency (where you can't fly to closest airport or strip), would they (Air Force, military or whoever) allow the plane to land on the Area 51 airstrip? Have there been any occurrences that we know of?

They absolutely will not allow you to land there, regardless of the emergency. I didn't post this as an answer, because I can't find (and I don't think there is) any formal procedure about this.

By the way if you are close enough to Groom Lake that it is your only viable landing site, you've already probably busted the no-fly airspace around that area and the cause of your emergency may very well be related to your proximity to it.

Good to know. Just curious things that I always thought I'd ask someone some day.

You can absolutely land in Area 51, as long as your aircraft has a circular wing.

No you 'could' in theory land at Homey AFB during an emergency, but you would be in very deep trouble for violating restricted airspace, trespass on a classified military installation, etc thereafter.

Having flown around the area a number of times, I can say that there are a lot of places outside the restricted area that would be easier to reach in case of emergency - several airports, dry lakes, straight sections of traffic-free highway...

Kinda depends on your opinion of Sidewinder missiles.

@RonBeyer worse, if you're close enough that it's your only option yet not inside it's no-go zone you're already in the restricted airspace of the Nellis ranges and almost certainly tracked by SAM sites and/or have some fighters escorting you.

I knew a guy, who knew a guy, whose A-6 Intruder was on fire and he landed there.  It might have been during a Red Flag exercise.  I don't remember details, I heard the story second hand about 20 years ago.  Anyway, these guys were Navy pilots with Top Secret clearances, yet they were met at the airplane by armed security, and were hooded for the duration of their short stay.  Apparently they were treated courteously enough, but they weren't messing around when it came to keeping things secret...

R-4808, the restricted area around Groom Lake, NV, is restricted at all altitudes.  It is also surrounded on multiple sides by other restricted spaces and MOAs.
No routes, low-altitude or high-altitude, go through the area.  No one has any business being near there to begin with, so no one will have any emergencies in the area.

Assuming a hypothetical situation where you have lost all controls and engines and your driftdown will bring you smack in the middle of Area 51.
I would imagine you would be very soon flying next to America's finest and if you are something like a Cessna 152 they would probably allow you to land.
Your chances of leaving ... now thats another story!

There is no way a C152 can end up within gliding distance of "Area 51".  The entire area is Restricted or MOA for at least 40 miles in every direction. There is always a more suitable airport, no matter where the plane is (unless it is a deliberate and malicious attempt to get to Area 51)

@abelenky and even if there's no airport within range, there are plenty of flat open spaces large enough to land a C152, from dry lake beds to reasonably flat terraces.

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How frequently do civilian aircraft have mechanical issues to which passengers are oblivious?
I know that aircraft are pretty well built and maintained, but I am certain that while flying these aircraft also suffer from some or the other mechanical issues. I believe redundancy plays a huge part in keeping these aircraft in air, but how many times are the passengers really oblivious to the problems? What are some of the most common problems that pilots are used to?

What do you mean by "civilian"? General aviation (also known as GA) (e.g. the DR-400 can transport 3 passengers + 1 pilot)? airliners? (note that military uses aircraft developed from airliners such as the VC-25 or the A330MRTT)

Civilian meaning ferrying passengers on commercial aircraft for which they are paying a price. American airlines, United etc.

thus you mean airliners. Also note that some airliner are really small one. You should precise inside the question aircrafts concerned (e.g. those certified to carry at least 19 passengers, jet-airliners,...)

@Manu H come on, you're being a bit over the top. It was very clear what he meant, you can't expect people with a passing interest in aviation to specify 19 seats or above...

@Ben I agree, when posting a question you don't necessarily know the best way to restrict it as you don't think about all restriction (e.g. aircraft that are not airliners nor military can transport passengers and can thus be concerned by this question). Comments are also here to help precise questions, as explained in the help center

I don't think you'll find a definitive answer because most will be just considered routine items, but if you're including non-safety-critical items then I imagine the answer is "lots". Passenger aircraft are huge, complex, mechanical devices with many many parts. It is accepted and expected that some of these things will occasionally fail.
Most of these can fail gracefully without impacting the flight in any way beyond a note in the tech log. Not only that, but lots of things can be known to have failed but still allow the flight to go ahead as normal.
You may wish to explore the idea of Minimum Equipment Lists. These provide exhaustive lists of items which can fail and flights can still be dispatched as normal. Note this isn't the same as an in-flight failure occurring and continuing to the destination - items in these lists can be failed before you even take off.
For example, here's one for the Airbus A320: https://fsims.faa.gov/wdocs/mmel/a-320%20r21.pdf
Everything listed in that document can be failed in some way, but a flight still operate as normal (with exceptions, as per the remarks column)
For example, and to highlight the level of detail, an Airbus A380 does not need to be grounded because the "PA In Use" notification light doesn't work.

Agreed, Just about every flight will end with something on the aircraft needing to be fixed, or deferred to be fixed at a later time.

I wouldn't be surprised to learn that no flight has ever taken off without at least one thing not working in some fashion or other.

related: What, exactly is “on the MEL”?

Back in the 1990s on 747-100/200 aircraft, the f.e. would be first into the cockpit and would review the maintenance log. When the captain arrived, the f.e. would brief him on the maintenance status. Occasionally the f.e. would say that we had a "clean airplane," meaning that there were no outstanding deferred items. Usually, though, there was at least one, more often than not more than one. Deferred items that were in the cockpit or controlled from the cockpit, would have a bright yellow sticker next to the item. Sometimes it was a colorful cockpit.

@JörgWMittag - like Terry said, occasionally it does happen on airliners. It's even more rare in (US) Military Aviation - where it's called a black-initial or black-letter, and it usually makes a news release when it does like this one

It used to be normal for the airliners of the day to have multiple non-critical fault alarms active at takeoff. Airlines tended to take the view that if an alarm is non-critical then there is no problem, no need to hold the aircraft back. Pilots complained that there were often so many that spotting a critical warning among them could become a problem. Pilots also often disabled them (especially audible bleepers, buzzers and such) to reduce the level of distractions. Keeping the level to manageable proportions is an important part of modern flight deck instrumentation design; the fault indicattions are still there, but not intrusive. Different airlines tolerate different levels of fault indication.
I was once a passenger in a venerable Dakota, still being operated by a commercial airline. Several rows of rivets were missing from the trailing edge of one elevator. Most had been replaced by twisted wire, but some holes were just left. It had evidently passed inspection nonetheless. Most passengers never noticed, and the trip was uneventful.
The general approach to passenger information is often, as they say, "what the eye don't see, the heart don't grieve over".

To say "multiple non-critical warnings active at takeoff" is incorrect. A writeup isn't a warning; if I have anything on the Master Caution active, we won't start the takeoff until it has been addressed. This answer far overstates how much may be wrong with a modern airliner. On the other hand, they're incredibly reliable machines.

@RalphJ Can you explain why a fuss gets made periodically - or certainly used to be - over the confusion to pilots caused by excessive numbers of such devices being active?

Can you reference where such fuss is made? Because I haven't seen much in many, many years. Airliners are complex, so there is necessarily many indicators in the cockpit, but all warnings, cautions and alerts are prioritized and colour-coded exactly so that it is easy to tell what is most important at any given moment. And have been for at least 40 years.

On a side note, a non-critical warning is an oxymoron, because warning means something that needs immediate attention. The other categories are cautions, alerts and memos.

@JanHudec Sounds like the issue has been sorted on modern types then, I lost touch while the "we really need to do something about this" voices were still strong. Many older cacophanous types are still flying with lesser airlines (especially overseas), maybe pilots here are lucky enough to be with the better ones. No refs while the Flight archive is down, sorry.


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When the winds aloft are light and variable, what wind direction and speed should I use for flight planning?
What do you input in a navlog for wind direction and velocity, when the wind and temp forecast says 9900+18? I know 9900 means light and variable winds less than 5kts but how do I determine the average wind direction to use for my navlog?

Welcome to aviation.SE!

Why not just consider the winds effectively calm?  If you want to be conservative, give yourself a 5kt. headwind.

Light and variable means there's no meaningful windspeed or direction, so you can just ignore it. For planning purposes, you can simply plan as if the wind was calm.
But, it's very possible that the winds will actually be stronger and more directional than forecast. You should check your actual track and times against what you planned, and adjust your navlog in flight as needed. That's one of the cross-country navigation skills that pilots are expected to learn.

The best technique when planning your flight is to assume a 15knot headwind ALL the time. This allows for climbs, descents, and delays, and works quite nicely.

"Best technique"?  Maybe the easiest, but hardly the best.


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What's the difference between "Nonstop Commercial Air Tour" and "Aerial Photography"?
I work for an FBO that has a LOA for Nonstop Commercial Air Tours, which are limited to a 25 statute mile radius of the airport. I was contacted by a man who is a semi-professional photographer who would like to be taken on a flight for the purpose of getting some nice pictures of mountains.
He says that because he is doing aerial photography that he should not be restricted to the 25sm radius per the exemption in 119.1(4)(iii). However, if this is the case, then all of our scenic flights conducted under the LOA would also be exempt, because the passengers always take pictures, and there would be no purpose in having the LOA.
So, what is the line between a Nonstop Commercial Air Tour conducted under a letter of authorization, and aerial photography?

Is it in section 1 of the FARs? If not, if I'm a fed looking at this I am inclined to see it as an air tour as "aerial photography" generally refers to the industry, not to what a passenger does during a flight. Just my thought.  Ask the customer for supporting documentation.

Short answer: as far as I can tell, an air tour implies photography, but photography doesn't imply an air tour. The regulations define various criteria for determining if a flight is an air tour, but there's no 100% clear definition.

First, the regulatory definition of "commercial air tour" is in 14 CFR 110.2:

Commercial air tour means a flight conducted for compensation or hire in an airplane or helicopter where a purpose of the flight is
  sightseeing. The FAA may consider the following factors in determining
  whether a flight is a commercial air tour: [...]

It's worth reading the "following factors", by the way.
Second, there's no formal definition of "aerial photography". See the Sapp (2007) interpretation (emphasis in the original):

In a 1989 interpretation, the FAA discussed the meaning of "aerial
  photography" [...]
  the phrase was not defined in the regulations [...]
  "aerial photography" connotes a condition where taking pictures or
  filming is done from the air

Third, the Ragland (2015) interpretation specifically mentions photography as one purpose of an air tour (emphasis mine):

Specifically, you asked whether §119.l(e)(4) allows persons to conduct
  commercial air tour operations, for purposes of sightseeing and
  photography, without obtaining either a letter of authorization
  (LOA) in accordance with §91.14 7 or a commercial operating
  certificate in accordance with part 119 of the federal aviation
  regulations.
You assert that the conclusion in a January 5, 2011
  interpretation issued by our office "appears to reinforce the need for
  Operators to apply for a LOA from their local FSDO to conduct
  'sight-seeing tours' within a 25 statute mile limitation under 14 CPR
  91.147." We agree.

Finally, the same interpretation says you can't operate a commercial air tour under the aerial photography exemption:

We further note that the exception in §119.1(e)(4) for certain "aerial
  work operations," such as banner towing, aerial photography or survey,
  and powerline or pipeline patrol, does not extend to air tour
  operations in which the primary purpose is sightseeing.

So, putting all that together - and remembering that I'm just SGOTI - it appears that:

Air tours within 25SM require an LOA and are assumed to include photography
"Aerial photography" is a separate activity from "sightseeing"
The FAA seems interested in the "primary purpose" of the flight

In your scenario, it sounds like the photographer is asking for a straightforward aerial photography flight: the primary purpose is to take photographs, not to get a tour of an area. And if the photographer actually makes money from their work, that's a strong indicator that they aren't just "sightseeing". But that's just my opinion.

The regulations (cited by @Pondlife) are pretty vague, so consider what the FAA is likely concerned about: who is put at risk and how it will affect ATC operations, and the typical usage of the two terms shows vastly different natures:
An air tour is frequently flown and nonstop, and each time the several passengers will be different members of the general public for the purpose of seeing (weather permitting) the same things with their eyeballs. If they happen to take photos to memorialize the trip, that is incidental.
Aerial photography/survey is generally a one-time flight directly to the area to be photographed, loitering over that area to get the photos required, and then returning directly. They typically have a single passenger who is a professional photographer specializing in aerial work and often a pilot themself, not a member of the general public.

I spoke with our POI at the FSDO and he said that the flight would be exempt since it's aerial photography. We're still limited to departing and arriving at the same airport. That doesn't completely answer my original question, but at least I know the flight will not raise any eyebrows at the FAA. Thank you for the responses.


text:
Are there regulations on building homes at the end of a runway?
I live next to a golf course (Butter Valley Golf Port) in Bally PA that has a paved single engine air strip that runs through a portion of the course.  Off the end of the runway (in one direction) perpendicular to the end of the runway is a single lane public road that runs in both directions.  I live on this road down the street from this same end of the runway. Currently on the opposite side of the road at this end of the runway is 80 acres of farmland.  A developer has submitted plans to build 236 condos on this 80 acres directly across the street from the end of the runway.  Are their regulations about building homes on the landing/take off flight path of a registered runway?  Where could I find these regulations?

There are some requirements, I don’t have them to hand but I think you’re going to be disappointed and the condos be will be regulations. Look up runway run off area requirements.

The real question is how hard will it be to get insurance for those homes, and what deed restrictions will there be on noise complaints. Those who purchase will likely not prevail in any complaint about noise seeing as they knew they were living so near the runway.

While the development is in the planning stages, it may be possible to design it in such a way that there is an open area such as a park, playing fields, or a wide central road with perhaps a grass medium for emergency landings extending from the runway end.  This may improve insurance premiums and help the airport and new development get along much better. Bringing the issue to a town council could be part of a permitting deal.  The pilots would appreciate it.

The FAA has regulations on the maximum height of obstacles around a runway (page 22):

The runway Obstacle free zone (OFZ) is a defined volume of airspace centered above the runway airspace above a surface whose elevation at any point is the same as the elevation of the nearest point on the runway centerline. The runway OFZ extends 200 feet (60 m) beyond each end of the runway.

...

The inner-approach OFZ is a defined volume of airspace centered on the approach area. ... Its width is the same as the runway OFZ and rises at a slope of 50 (horizontal) to 1 (vertical) from its beginning.

Does the inner-approach OFZ apply here?  The FAA manual says it "only applies to runways with an approach lighting system", which I suspect the airstrip in question does not.

There are several more zones, depending on airport size. That's for the OP to figure out; he just needed to know where to find the regs.


text:
What is the make and model of this plane?
I came across this picture taken in the late 1920s. Could you please help identify the make and model of this plane. Thanks.

Some context would help, such as where was the picture taken, maybe who was the photographer, etc.

It was taken in 1929 in Burbank CA area.

That info helped. Looks like a Travel Air 2000, but without the prop spinner.

Thanks, Juan. It certainly looks a lot like it. I wonder what is in the bottom of the fuselage in the picture I posted. Some kind of radiator fin or just an open trap door?

https://youtu.be/AVQcRLPt5EIthis video confirms in. Thanks again, Juan.

Nice video, that looks like a sweet ride. At the bottom is a radiator indeed. The aircraft was powered by a Curtis OX-5 (https://en.wikipedia.org/wiki/Curtiss_OX-5) or OX-6 engine (can't tell from the picture) and those were water-cooled engines. You're welcome, and don't forget to mark it as the accepted answer. :)

It could have been a Swallow too. The propeller and wheels are similar.

The engine, exhaust and cowling are different, so are the wheel hubs.


text:
Why does pressure remain constant in the boundary layer?

From Fundamentals of Aerodynamics by JD Anderson.

It can be shown experimentally and theoretically that the pressure
through the boundary layer in a direction perpendicular to the surface
is constant. That is, letting pa and pb be the pressures at points a
and b, respectively, in Figure 1.47, where the y-axis is perpendicular
to the body at point a, then pa = pb.

But, there exist a velocity gradient on the boundary layer. Doesn't this violate Bernoulli's equation? Does this assume pressure remains almost the same in the viscous region or I am missing something?

There does exist a velocity gradient within the boundary layer.  However, the boundary layer, being a viscous phenomenon, does not obey the Bernoulli equation, which is what trips up our usual intuition
So Where Does Bernoulli Come From?
Bernoulli is a simplification of the Euler equation (which is a simplification of the Navier-Stokes equations).  The Euler equation is an inviscid formulation of the Navier-Stokes equations, and Bernoulli further neglects rotationality and states that the total pressure of a fluid is constant (in steady flow, along a streamline), giving the following expression that we're familiar with:
$\frac{1}{2}\rho v^2+P=const$
This works great outside of the boundary layer, in incompressible (typ. Mach < 0.3), irrotational, inviscid flow...which, conveniently, helps us to understand a good many things that we're interested in (e.g., model airplanes, sailplanes, some GA aircraft, etc.).  However, it has its limits, and one of the many tricks of aerodynamics is knowing the assumptions of your models and when they can and cannot be applied.  This is why panel methods, relatively low-fidelity fluid modeling techniques, are still being used in hydrodynamic modeling.  So long as you don't violate their assumptions, you have a body-fitted model that is faster than more modern finite element or finite volume methods and still gives an accurate result that can be used to predict body loads (and, thus, do performance analysis, etc.).
OK, but why is the pressure still constant?
To the point, Anderson states that pressure is constant through the boundary layer along a line normal to the surface of the body (or airfoil, in this case).  The normal part is important: it means that pressure is not necessarily equal along the length of the airfoil.  Let's look at a small element of fluid moving along the body surface (below) to play with this:

So, pressure gradients drive flow.  If there was no pressure gradient along the length of the airfoil ($P_{right}=P_{left}$), the flow velocity would be zero.  This is not the case, and flow is moving from left to right, therefore, $P_{left}>P_{right}$.  Furthermore, as a result of viscosity, we have a velocity gradient as a move away from the body (e.g., low/zero flow velocity close to the body and increasing flow velocity as we move away from the body through the boundary layer).  This implies shear along the top and bottom of the fluid element in the picture, which corresponds to the pressure difference we mentioned.  However, there is no vertical motion in the boundary layer (there can be in a turbulent boundary layer, but I'm assuming a laminar one for the purposes of this explanation) and no vertical shear.  As a result, $P_{down}$ must equal $P_{up}$ on this element.  If I think with a Newton's 3rd law kind of mindset, the fluid directly above and below this element would feel the same pressure and so on and so forth until you get to either the edge of the boundary layer or the surface of the airfoil.  The assumptions for this fall apart outside of the boundary layer, since there is non-negligible fluid motion towards/away from the airfoil, so that's why I'm stopping the analogy at the edge of the boundary layer.
Hence, along a line normal to the surface, since this does not imply that $P_{up}$ on this element is equal to $P_{up}$ on the element to its left or right, the pressure is constant throughout the boundary layer.
Other references: https://web.mit.edu/hml/ncfmf/10FBL.pdf

I appreciate the in depth answer! One question : If the velocity across the boundary layer isn't constant, why is the pressure? Like at the edge of the BL the air is moving faster, and really close to the wing the air is moving slower. I understand that Bernoulli's equation doesn't work in this scenario, but I'm confused as I found this on google :

"Bernoulli's equation cannot be directly applied to viscous flow because, in viscous flow, the motion of the fluid particle is constant. Hence, we need to convert the viscous flow into the Navier-stoke equation and then Bernoulli's equation can be applied to it."

@Wyatt - Hopefully this helps: Bernoulli is derived from the conversation of energy, but it neglects several forms of energy transfer (e.g., viscosity, rotation, etc.). If I think of the boundary from an energy point of view slower/faster air has different kinetic energy and, if we neglect everything Bernoulli does, the only result of that must be a change in static pressure. However, if we don't, we see that change in kinetic energy is actually due, most notably, to viscous interactions with the nearby surface. You might think of Bernoulli like doing physics without accounting for friction.


text:
Why are biofuels usually blended with standard jet fuel when used?
When biofuels are used in both demonstration and commercial flights, it is common for them to be mixed with standard Jet A fuel. Is this due to safety reasons, cost or due to specific properties (e.g. freezing point of biofuels) that may not enable them to be used solely all the time?

Welcome to aviation.SE!

What are you basing that statement on @LinfanSiddiqi? The test I've seen has been using straight biofuel. Often one engine will be run on biofuel and the other on Jet A1, is that what you're thinking of?


text:
What do these explanations for propellor RPM increases mean?
I have read in a book that if the engine RPM increases while descending, the probable causes are:

Engine transfer bearing leaking excessively
Excessive friction in blade bearings

I am not able to understand these reasons.
Can someone explain "engine transfer bearing" and what these two reasons mean?

Welcome to aviation.SE! Your question appears to be related to a Pilot's Operating Handbook or Line Maintenance Manual, in which case more details about the make&model would be welcome.

The title talks about propellers, but you tagged this as [tag:jet-engine]. Could you clarify which type of engine this is about? Maybe you want [tag:turboprop]?

Could you please expand point 2. ?

Your title suggests that you may be troubleshooting a problem on a specific airframe. If so, more details would be helpful.

Not talking about specific airframe/ engine, as I am a student and studying about propellers!

Could also be another explanation. What happens if you maintain power, but descends  ? -> engine will run faster

The troubleshooting section from the Hartzell Propeller Owner's Manual No.411 states:
B. Engine Speed Varies with Flight Attitude (or Airspeed)
   (1) Small variances in engine speed are normal and are no
       cause for concern.
   (2) Increase in engine speed while descending or increasing
       airspeed:
       (a) Non-feathering ( )(A,B)1 series propeller:
           1 Governor is not increasing oil volume in the
             propeller.
           2 Engine transfer bearing leaking excessively
           3 Excessive friction in the blade bearings or pitch
             changing mechanism

Reasons 1-3 relate to the propellers inability to adjust its blade angle to maintain a constant RPM when descending and airspeed is increased on non-feathering propellers.
The transfer bearing allows governor controlled oil into the crankshaft interior then to the propeller hub. If the bearing is leaking excessively the oil may be leaking back into the crankcase and there may not be enough oil pressure going into the hub to increase the propeller blade pitch and slow the engine down.
If there is excessive friction in the blade bearings the propeller blades may not move freely within the hub even when adequate oil pressure is supplied by governor and oil system.


text:
Why does an Exhaust Gas Temperature (EGT) gauge require a power source?
Why does the EGT gauge on jet engines require bus power if thermoelectric voltages generated by thermocouples are sufficient to move the needles?

What do you mean by drive the pointer ?

Well if only it's as simple as a thermal couple and a needle. Welcome to 21 century man!

The thermocouple voltage is a DC millivoltage. Presuming you’re talking about an analog gauge, there simply isn’t enough potential to “drive the pointer.” As such, that small voltage is usually amplified. The amplification requires that a larger power supply be used.
For a digital gauge, that millivoltage is capable of being read by a microprocessor, but the rhetorical question of “What powers the microprocessor?” Should be enough to resolve the rest of the question.

Why isn't there enough potential to drive a (sufficiently-light) pointer?

I suppose a sufficiently light pointer with sufficiently minimal resistance would work, but I honestly don’t know what those requirements might be. Generally speaking, amplifying if externally gives you more distinct control (and probably accuracy) over something like what you’re suggesting.


text:
What is the stalling speed of a Cessna 172SP at an altitude of 2000 feet?
What is the stalling speed of the Cessna 172SP if the temperature is +11 degrees Celsius, the power is off, the CG is at the forward limit, the flaps are at 0 degrees and the altitude is 2000 feet?

this looks like a quiz question. could you tell us why you are unable to answer? where are you encountering problems?

What is the AOA? It is important to realize that a plane can stall at any speed, what matters is when you have separation of the flow from the wing, which occurs at a certain angle of attack, not necessarily speed.

@RonBeyer stall speed is a well defined quantity

@Federico For level flight, yes, but increase the load factor (turn while staying level) and it changes. This is a major cause of accidents called an accelerated stall/spin.

You should be able to determine the speed from the Pilot's Operating Handbook, which is available online. See page 5, and Section 5.
http://www.airilm.com/wp-content/uploads/172S-POH.pdf

Downvoted for providing facts? Really?

Looks to me like this is exactly the answer this question deserves. +1

@CrossRoads No, for providing only links.

PDF Document was not copyable - try it yourself and see.

If it's not copyable, you can type it out yourself... in this case, screenshot the chart and show how to determine the speed?

@CrossRoads we (SE network) prefer when answers contain the relevant information, and do not require people clicking on links. if you cannot copzy-paste from the pdf, then you have to re-type it by hand. (or screenshot if a chart)

Fine - 48 knots KIAS, 53 knots KCAS

Yes, like the one I referenced.  Or the one in the plane you are flying.


text:
What is the best route for my 18 year old son to become a pilot with a major airline?
What is the cheapest and most effective way for my 18 year old son to become a commercial pilot with a major airline?

Sorry, this is way too broad, we can't offer career advice.

Why not?  The answer is easy.  Military.

At this moment in history I think there's a valid concern that he will lose his job to robots within the time span of his career.

We usually can't answer these questions very well because so much depends on your personal situation. Which country are you in? Is your son willing and able  to move to another country? Does he want to get a degree or not? What financial resources do you have? Is entering the military an option? Etc. You might get a better response on a discussion board; as a Q&A site, we try to find the single best answer for each question and there may be ten different answers to this one.

Robots?  The cert process is so glacial, especially on the airline side, that this is very unlikely in our lifetimes.  Single pilot airliners in 20 years?  Maybe.  But you will see it in GA and the corporate world long before.

Look for a community college with an aviation program, they're quick and VERY affordable. I attended Iowa Lakes Community College, I was able to get my Private, Commercial, Instrument, Multi-Engine, and Instructor ratings in 2 years for $38k. DO NOT send him to a large university like UND, the programs are insanely overpriced and they take 4 years solid. At Iowa Lakes, you can get done as fast as you can, people have gone from student to instructor in a year, it all depends on you, at universities you HAVE to stay all 4 years which is a killer in an industry so heavily reliant on seniority. I have the exact same ratings as a kid coming out of UND only I have 1/4 his debt and I'm probably already a captain at a regional when he first gets to the airlines. Airlines are REALLY hurting for pilots, this is absolutely the best time to be a pilot.

The shortage of pilots in N America is so severe, made much worse by the stupid Colgan law requiring 1500 hours for regional ops, that the regionals frequently cancel flights and/or park aircraft due to lack of crews.  The quality of new hires has been declining.  Air Wisconsin and others have had to increase their training resource allocations, adding sim time etc to cope with pilots not able to get through a type course in the traditional 7 sessions + check ride.  In Canada there isn't the silly experience minimum, but the shortage is starting to be felt as severely as the US.

Son will be attending Broward College Aviation, reading shortage is only in Very experienced pilots.


text:
Do you have to lubricate the shock strut?
I have a school report about the lubrication on the shock strut and I was wondering if there is a specific type of lubrication they apply it on.
This is for Cessna 150-152

cessna 150-152.

What do you mean by lubrication?  Greasing fittings?  Or applying something to the strut chrome?

I heard that they apply something on the outside part of the shock strut or some kind of a fluid?

Oleo struts and brakes used on light aircraft use MIL-H-5606H hydraulic fluid (the red stuff) as the internal damping agent/lubricant (be sure to check the manual anyway). It's a normal practice to clean the exposed chrome of the shock strut (it should be done with the tail held down to extend the strut all the way) with a clean cloth, then wiping it with a cloth with a little bit of 5606 to leave just a very light film to help lube the scraper and seals the next time the strut compresses (once that's done there is the film of internal fluid left behind by the seals).
The biggest enemy of oleo struts is silica particles (which are very hard) from outdoor dust which sticks to the chrome surface because of the fluid film left behind by the internal seals.  The silica collects in the seal cartridge and acts like lapping compound, accelerating wear (this is why desert operations are the toughest environment overall on any airplane).
As the strut ages and the seals wear and slowly start to leave behind more fluid each time the strut extends, dust collects faster and the whole process speeds up, so the strut should be kept clean as much as possible depending on how dusty the local environment is.
If it's your own plane, you should learn to do the published procedure yourself, because nobody else is going to do it between annuals.  If you're renting the plane, that's the owner's problem, and you just do your normal walkaround inspection.

By law, the FAA requires the POH to provide basic servicing instructions and approved lubricant. The exact information provided depends on the year of aircraft, older aircraft having less information (the FAA became stricter over time).
See: C150 POH Manual
For the C150-152 the Pilots Operating Manual (POH) provides all necessary basic maintenance information in two places - "Servicing Intervals" and "Servicing Requirements" (I'll leave it upto you to see if the nose strut is applicable).
There is a fundamental rule all teachers and instructors tell new or potential pilots, "... READ THE MANUAL!"
I am an A&P and Pilot. By FAA law the POH must provide the proper servicing lubricant type - READ THE MANUAL. The information is located on the next to last page of the manual I cited! It is against the law to use any lubricant not approved by the mfg or FAA. Motor oil is commonly wiped on the strut but unless there is a SB (service bulletin) from the mfg that is not legal.
The FAA prohibits the unauthorized mixing of dissimilar brands or types of lubricant except for motor oil (By law, motor oil must be able to be mixed). In this case the POH provides the authorized lubricant to be used on the strut.

The Manual only discusses checking the strut for proper inflation. Otherwise, it refers one to the Maintenance Manual for "complete servicing, inspection, and test requirements" which are "available from your Local Cessna Service Station".

The approved lubricant for the strut is located on the next to last page of the manual I cited. READ THE MANUAL!


text:
Is there a limit to how large an airplane wing can be?
There are some agreeably large planes out there, like the C-5 Super Galaxy. But how big can these planes' wings really get?
The heavier the plane, it is usually larger, and with size of the fuselage comes size in the wings (most of the time). But is there a limit to how big you can make your wings?
If you make your wings so big that they're 6 feet thick and an absurd length long, say, for a colossal plane, will those wings provide enough lift? I mean, if the wing gets that big, It not only has to lift the plane, but its own weight then becomes a concern. But, with that weight comes the size. Another issue, is how the aerodynamics work on such a crazy big plane.
The thicker the wing, the more air is contacting the wing. This causes more resistance on the wing at a given chunk than a smaller wing. The question comes from seeing several shows that depict planes so large they're like flying cities, and it just doesn't look realistic to me, the sheer size of those planes.

Closely related, perhaps even a dupe?

No, my question is actually concerning the wing size, if the wings will work the same at such a size in comparison to the general smaller wings. But thanks for trying to help clear things up!

The big flying boats had wings a guy could walk through. Assuming that wasn't the tallest guy, the wing would still need to be about 5-6 feet thick at the thickest part. And they flew and flew well.

If the wing grows large enough relative to the other parts, you end up with a flying wing airplane. At the latest, then your question becomes a dupe.

No, there is no theoretical limit to the size of a wing. You could make a wing big enough to lift the entire Earth (assuming, of course, you somehow had an atmosphere to fly it in).
There are, of course, many practical limitations to wing size. The lift a wing develops is proportional to the square of the scale of the wing, all else being equal. However, the weight of the wing (and the rest of the airplane it's attached to, for that matter) is proportional to the cube of the scale. So, if you double a plane's size, the lift developed by the wings goes up four times, but the weight goes up eight times. So, in that case, the wings would need to be even larger compared to the plane in order to lift the added weight. This is referred to as The Square-Cube Law (Wikipedia, Aerospace Research Central, TVTropes). You eventually reach a point where there are no materials strong enough to withstand the stresses imposed on such a massive wing.

This is wrong in part. The weight is in fact proportional to the square of the scale, not the cube. A plane is mostly surface and stiffening members. The wing loading, and hence the stiffening stresses throughout, are the same regardless of scale. Only the volume of empty space genuinely cubes up. The ARC guy seems to know more about airships (whose lift does depend on that empty space), but he is partly right about aeroplanes because the stiffening gets increasingly difficult to manage and weight creep does set in.

The TVTropes link is bang on.

@GuyInchbald I'm curious about this. The scale, by you mean the size? Isn't there several other factors such as the aerodynamic efficiency of the wing, that make it impossible to simply relate the weight as being proportional to the square of the scale? I may be wrong on this.

hi @Wasabi  It's straightforward, and explained (at incredible length) on the three familiar links given.

@GuyInchbald No, the weight of anything is in fact proportional to the cube of the scale. If you double the size of the wing, the structural members double in width, length, and height. That's eight times the volume, so if density doesn't change, that's eight times the weight.

@HiddenWindshield, not everything has a weight proportional to the cube of scale.  For example, over a reasonably large size range, the optimal wall thickness of a cylindrical tank is effectively constant, giving a weight proportional to the surface area (ie. the square of scale).

@GuyInchbald Statistical analysis shows that the exponent of scale for airplane weight is between 2.3 and 2.4. So both of you are only partially right and there is indeed a higher mass increase with scale than the increase in wing area.

@Mark Generally, at least in my experience, when you're talking about a hypothetical (such as wings the size of the Earth), then "scale" simply refers to blindly making things bigger (or smaller), as in a "scale model". That's the sense I was using in my answer. If you're going to design something at a different size, then, yeah, the weight isn't going to be exactly the cube of the size.

@Wasabi, you are right, it is not quite that simple. The basic scale effect is a structural one which becomes increasingly difficult to engineer at larger scales, hence the intermediate figures noted by Peter Kämpf. Also, the Reynolds number affects the aerodynamics, so an exact scaling of the external profile is probably not what one would do in practice. Then there is the handling responsiveness, which also gets harder as it scales. You might like to ask a more general design question about scale effects, than this one.

@HiddenWindshield Your intuitive assumption of scaled-up cross-sections is in fact quite wrong. For example wing loading remains nominally constant, so skin thickness remains constant and large aircraft therefore have proportionately thinner skins. Similar issues mean that the total spar weight scales with the square law too. The difficulty lies in keeping the wing rigid, with the internal structure becoming more complex and spider-webby (sometimes referred to as increasing cellularity); this is the structural aspect that gets harder to engineer at scale.

Now that this question has been marked a duplicate, I have posted a fuller answer over there, i.e. https://aviation.stackexchange.com/questions/27401/is-there-a-maximum-possible-size-for-an-airplane

@GuyInchbald Well, I think we're just going to have to agree to disagree on this one.


text:
How long does it take for a new FIR to be created by ICAO
How long does it take ICAO to create/approve a new Flight Information Region(FIR)?
Occasionally FIRs are split because of various reasons. The question is how long ICAO takes to approve the new FIRs creation.

It’s the ICAO Council that would approve a Flight Information Region (FIR). The Council meets three times a year.
You can have a look at Doc 7559/11 - Rules of Procedure for the Council, at the following rules:

Rule 22 A Provisional Work Programme of each session of the Council
shall be prepared by the Secretary General after consultation with the
President and presented to the Council for approval. The presentation
to the Council should normally, and wherever practicable, be made
during the preceding session. The Council should indicate the priority
which it attaches to the consideration of the various items in the
Provisional Work Programme.
Rule 23 In preparing the Provisional Work Programme, the Secretary
General shall include therein:
a) subjects which require consideration by the Council by virtue of
provisions of the Convention or other international agreement;
b) subjects to be considered by virtue of decisions of the Assembly or
decisions taken by the Council at a previous session;
Rule 25 The Order of Business for each meeting shall be prepared by
the Secretary General and approved by the President.
Rule 33 A majority of the Members of the Council shall constitute a
quorum for the conduct of the business of the Council.
Rule 52 In the event of a tie vote, a second vote on the motion
concerned shall be taken at the next meeting of the Council, unless by
a majority of the votes cast the Council decides that such second vote
be taken during the meeting at which the tie vote took place. Unless
there is a majority in favour of the motion on the second vote, it
shall be considered lost.

While this may be factual, it doesn't actually answer the question. Is it guaranteed that a FIR split will be addressed and approved/denied at the very next meeting, or might it carry on for discussion over a couple of meetings? A quote from the ICAO rules would help support your answer.

Edited, thank you.

Still doesn't really answer the question of "how long". Or, if it does, it's very unclear to me. This looks like it could be at the next meeting, but that (rule 22) it might not even be addressed at the next meeting ("normally and wherever practicable...") and if it is, what you've provided doesn't show that there must be a vote at this meeting - motions can be tabled, or, if it is voted on, rule 52 states that the normal course of action is to vote at the next meeting...

The only real measure, IMHO, would be to show some metrics of actual past FIR split requests and how long they actually took to be approved/denied.


text:
Airline flight scheduling method differences
What are the differences between American major mainline passenger airline scheduling policies?
Presumably, each airline runs a model or optimization problem for determining

where (markets/airports),
when (timing of the flights throughout the day), and
how many seats (plane capacity).

Are there any specific examples of different scheduling policies, methods, or algorithms among airlines - within the context of each airline doing the best it can to match its schedule to market demand, according to its business plan and strategy?

I suspect they're a closely guarded secret beyond the vague principles you outlined.

Although this question is on-topic, i doubt it will ever be answered satisfactorily.

Although marginally on-topic, the focus of this question is the use of business intelligence (or data mining) algorithms for flight scheduling. Note that even if the model is similar, different inputs (base location, loyal customer behavior, cost breakdown) would result in different output. Unfortunately, a vague understanding would require reading at least several chapters of a relevant book. Voted to close.

Regarding your second last paragraph, it is called codeshare. There has already been a question for that.

There are many academic papers available for general airline scheduling topics. Airline flight schedule planning is a huge topic, existing within the more general field of Operations Research. The models and algorithms used are not simple by any means, and thus there could exist many kinds of differences between the methods used by each of the different airlines.
Considering such models are part of how airlines gain a competitive advantage, specific airline methods, at least for now, are proprietary information.  Perhaps this will not always be the case, but it would take a change in the  way the airline industry operates for this type of information to be publicly available.
That being said, the data about the output of those models are freely available, collected by the U.S. Government (see the Bureau of Transportation Statistics).
Theoretically, one could mine the available data to reverse-engineer some differences, but these will be theories at best.


text:
Why is Germany not able to read data from the Boeing 737 MAX black boxes?
It is my understanding that Germany stated it does not have the capacity to read the new software, declining Ethiopia's request:

"The French announcement resolved uncertainty over the fate of the two
  recorders after Germany’s BFU said it had declined a request to handle
  them because it could not process the new type of recorder used on the
  737 MAX jets, in service since 2017."

Does anyone know which requirements were missing?

This news article (in German) includes a mention that the black box was using newer software than the BFU has the capability to read out:

Das Gerät habe eine neue Software, die an der BFU nicht ausgelesen
  werden könne.

Thank you. That is what I was curious about -- as to why they are not able. Contrary to France.

@ted don't forget to mark nengel's answer as accepted!:)


text:
Will the Boeing 737 MAX 8's software update require recertification of the aircraft?
Will the upcoming software update for the 737 MAX require the plane to go through a new certification like a new plane?

Nope
Updates like this are generally deployed under an Airworthiness Directive ("AD") and in this case will likely be required although not all AD's technically are. AD's are issued against Type Certificates or serial number ranges, or possibly even individual parts. They are publicly published and when it becomes available the FAA will post it here.

Certifying a new airplane, or even a new version of the type as with the MAX, is a huge deal. It does not make sense to go through the whole thing again just for a fairly minor change.
However, once a plane is certified, the entire design and configuration is fixed. Any changes have to be approved to allow the plane to be considered airworthy as an example of the certified type. The manufacturer will have to show that any change will either not change the basis of the original certification, or if it will, to justify how it will maintain at least an equivalent level of safety to the original configuration, and meets the regulations.
Boeing will certainly have to test a software change to MCAS, just as with any change the modifies aircraft behavior. The FAA will have to sign off on the change once they review the certification and any test data and find it meets regulations. For some tests the FAA requires that an FAA inspector be on board to witness the test, and given the profile of the situation and the scrutiny being applied, that may be the case here.
Of course, if an aircraft is operating under a different regulator, such as EASA, that regulator will also need to agree that the modifications meet regulations. For small changes they may defer to the main regulatory body, but again with the scrutiny in this case, other regulators will probably be sure to review the changes very carefully before extending their approval.
In cases like this where the regulator believes safety is an issue with the existing configuration, they can issue an Airworthiness Directive that mandates a certain inspection or change. The AD will define when this must happen, and if not accomplished by the deadline, the plane is no longer considered airworthy. The deadline could be a hard date, or within a number of flight hours/cycles.


text:
On old sectional charts, what was the purpose of the domestic ADIZ regions and what was the difference between a "Defense Area" and an "Open Area"?
Looking at an old US sectional chart from 1956, I noticed a few oddities around where Air Defense Identification Zones (ADIZs) were placed.
Compared to modern airspace where the US ADIZ is strictly off the coast and along the borders, there appear to have been additional land-based ADIZs dividing the country up into three parts. There was also a large ADIZ centered over Albuquerque. They also seem to have made a distinction between a "Defense Area" and an "Open Area".
What was the purpose of having an ADIZ inside the country? What's the difference between an "Open Area" and a "Defense Area"? And just what was so special about Albuquerque?

For the Albuquerque ADIZ, possibly https://en.wikipedia.org/wiki/Los_Alamos_National_Laboratory .  For the central open area, everyone knows there's nothing there but "flyover country" anyway...

It looks like this was set up to defend the Louisiana Purchase...

You can find the old 1950s regulations in the November 1, 1955 Federal Register. There's nothing special about that particular edition; I just happened to find them there first. The definitions of ADIZ and Defense Area are the same there as they are in the current FAR Part 99. In particular, a Defense Area is "any airspace of the contiguous United States that is not an ADIZ in which the control of aircraft is required for reasons of national security." Today, all United States airspace that is not ADIZ is Defense Area. The last part of the definition, about control of aircraft required for reasons of national security, is an oblique reference to SCATANA or ESCAT. In other words, a Defense Area is an airspace that is not ADIZ, but in which SCATANA or ESCAT may be implemented.
We also get the definition of "Open Area" from there, and it is essentially an area that is neither ADIZ nor Defense Area. In other words, an area where SCATANA will not or cannot be implemented. This area doesn't exist any more, but maybe it made sense in the 1950s, at a time when defense strategies were limited and the greatest threat was that of enemy bombers attacking the coasts rather than ICBMs attacking anywhere. It means that the air defense of the country was concentrated on the coasts within range of offshore enemy aircraft carriers (or wherever they were expecting attacks to come from).
So, the Defense Areas were the areas where attacks were expected to happen, if they were to happen, and were protected around their perimeters by ADIZ's. The Open Area was an area that was left defensively open because it was out of range (or something, like maybe the government hated the citizens of Miami?) of an expected air attack.

Originally they were zones to protect Americas nuclear testing areas and other key military interests. The Albuquerque area was likely there to protect Los Alamos Laboratory and other related nuclear assets of the era.
This report prepared for congress (on a slightly different topic) has some notes on this in the "History" section.
They explain an ADIZ as:

An ADIZ is a designated area of airspace over land or water within
which a country requires the immediate and positive identification,
location, and air traffic control of aircraft in the interest of the
country’s national security.

Which does not necessarily limit it to border monitoring. The modern ADIZ is large a border related zone but that was not always the case.

In 1948, the U.S. Air Force designated several offshore areas as
“active defense areas” or “defense zones.”3  From these, the first
ADIZs in the world were established in 1950, under an Executive Order
directing the Secretary of Commerce to exercise security control over
aircraft.4 Various defense zones were redesignated as ADIZs.5  The
present-day U.S. ADIZs, including the contiguous U.S. ADIZ, the
Alaska ADIZ, the Guam ADIZ, and the Hawaii ADIZ, are codified in Title
14, Part 99, of the Code of Federal Regulations, along with the
procedural requirements for flights operating in these designated
areas. They are predominantly located over water and typically do not
extend to the shore, leaving a narrow strip of sovereign airspace
parallel to the coastline that is not within the ADIZ.

The citation for the above paragraph explains it better (bolded for emphisis)

At the time, U.S. ADIZs included offshore regions stretching from
Maine to North Carolina in the Atlantic, and from the U.S.-Canada
border to waters off the Baja California in the Pacific. Additionally,
several over-land areas were designated as ADIZs, mostly along the
west coast and south of the U.S.-Canada border, but also above
interior lands around Albuquerque, NM, and Knoxville, TN, as part of
national security efforts to protect key nuclear research facilities
in these regions. The over-land ADIZs no longer exist. For a time,
portions of the special flight rules area (SFRA) around Washington,
DC, established after the 9/11 attacks in 2001, were designated as an
ADIZ, but this airspace is no longer referred to as such.

This map just pre dates the deployment of the Distant Early Warning System in the north and various Nike Missile Sites that were put on either coast but you can see how the American costal strategy was shaping up in a post WWII country which is interesting.
As radar became more prevalent at local facilities (think class B/C/D approach control as well as regional centers) the need for specialized interior radar was far less and those duties could be off loaded to the local facilities

My understanding is that the Trinity test site was only used once.  I would suggest that the Albuquerque site was set up to protect other nuclear-related assets such as Los Alamos National Laboratory and Sandia National Laboratories.  Wikipedia has good pages on them.  A relevant question would be "did the ADIZs exist in 1945 and if so, where were they located?"

@quietflyer ill update to reflect, my understanding is that most stuff was tested in that general area

Yes actually the White Sands Proving Ground does encompass the site of the Trinity test and they may have wished to protect that as well.  As far as actual atomic/ nuclear tests conducted after Trinity, I'm not sure, all the ones conducted within the US may possibly have been in Nevada.


text:
Why do many commercial aircraft have a red circle on the wing?
Many commercial aircraft operated by japanese airlines like JAL and ANA have a red circle on the wing. Look:

Source: Airliners.net
And on this ANA plane, also:

Source: Airliners.net
Why do they have that red circle there?

This is a genuine question and does not deserve all the downvotes. (Although it's an easy/naive one)

That would be the Japanese sun symbol which also appears on that nation's flag. You can also see that symbol on the tail of that JAL 777 on top.
Same as the Japanese Flag:

A Google image search for "Japanese air force" will show that red circle somewhere on every aircraft pictured.

May be another example:
Emirates airline:

and the flag of the United Arab Emirates:


text:
How is stability ensured with bulk-loaded cargo?
According to this question especially smaller airlines often don't use ULD in the cargo hold. But wouldn't that be dangerous for the stability of the aircraft? Won't the cargo move and unbalance the aircraft?

You can simply tie down the cargo to prevent its movement. Most planes have nets that subdivide the bulk cargo compartment, so as to prevent movement of the baggage. For example, the following image shows the cargo hold of a B737 with dividers.

Image from airport-data.com Photographer:  Nick Taylor Photography
The ground operations manual of a carrier gives the following procedure for securing loads in A320:

1.1.4.2.1. Load Securing A321 (bulk loaded)
The divider and door net in each compartment must be closed at any time. Additional tie-down is normally not required except for individual items of load which by their nature, shape or density may constitute a hazard. They must be restrained, which can be achieved by filling the cargo hold or net
  section volumetrically, or by tie-down.
... Packages weighing more than 150kg shall be restraint or individually tied-down. Single packages should be tied-down. Tie-down of loads to aircraft structure is achieved by straps or nets connected to the tie-
  down points located on the cargo hold floor.

So what would happen if I would want to transport a large container with liquid cargo? Do I have to take extra precautions to prevent sloshing?

@ROIMaison: This is probably the biggest liquid cargo carrying aircraft.

@JamesKPolk, This is another case, for the fire fighter aircraft the operator can place any baffles or things alike to prevent sloshing, whereas in the case of commercial cargo this might not be the case

Just a guess, @ROIMaison, but I'd say that containers approved for air-shipment of fluids include baffles to reduce sloshing.


text:
What is the meaning of T/O Thrust => TRQ / N1 in a flight log?
I work at a software company which builds record-keeping software for aviation.
What is the meaning of TRQ / N1 in a flight log, under a T/O Thrust header? I imagine it refers to torque at N1 (but in my limited experience, I have rarely encountered instantaneous torque as a relevant measure in aviation so I'm suspicious).
What is the meaning of TRQ / N1? Is this, like N1, expressed as a percentage?
(Indeed, we have a close relationship with out clients and can ask them, but answers sometimes take time and I prefer to be proactive and know more than the bare minimum.)

@Federico That in itself is useful information.  I assumed these were industry-standard terminology. I edited to add more context if it helps.

Torque is used extensively as a power setting and limiting indication in turboprop applications.

@JonathanWalters Thank you for noting that!


text:
What is the maximum side slip angle that can be achieved by a F-16?
During which flight regime is maximum side slip needed (apart from take-off and landings in cross winds)? I have learned that during a knife edge maneuver, the side slip angle plays a crucial role in maintaining the flight path angle.

What is the maximum side slip angle that can be achieved by an F-16?
And if possible, how does the F-16 compare to other planes of different roles?

I'm voting to close this question as too broad: side slip angles vary a lot depending on airframe design. We cannot answer for general aviation and civilian planes. You may wish to limit your scope to, let say, civilian aerobatic aircrafts only.

@kevin If we take off the last sentence and go with the F-16 in the title it should be focused enough.

I'm not sure that the sideslipping technique would be used in crosswing landings in a jet like the F-16.  Of course whenever the wheels are on the ground, if the jet is continuing to travel down the runway centerline in the presence of a crosswind, then some sideslip could be said to be happening, but I suspect the question is meant to ask about in flight.

I mean possibly 10° of beta could happen but 10° of beta (sideslip angle) is an extreme and unusual for an F-16. The Aileron Rudder Interconnect (ARI) automatically provides rudder input according to pilot roll input to reduce sideslip during turns

Calculations would get pretty complicated if you want to do a force analysis on the knife-edge pass to see how many sideslip is required to complete such move.
You would need wind tunnel data of Mach 0.6 from NASA TP-1538 to begin with: https://ntrs.nasa.gov/api/citations/19800005879/downloads/19800005879.pdf
First, get the total body X axis and body Y axis forces by calculating CX and CY using the below formula and multiply dynamic pressure and reference area. Add thrust force to the X axis too as it also plays an important role in keeping altitude.

Then cast the body axis forces onto the earth Z axis for a compensation of the weight of the aircraft.
I would suggest using simulation libraries such as Matlab or JSBSim to do this.
An RL HUD video of F-16 performing knife-edge starting from 0:21, showing a sustained sideslip angle of 11 deg with a steady altitude:


text:
Is the A330F main deck cargo compartment pressurized? If not, what is the purpose of the structural cargo access door?
I know there is a related question already asking if cargo holds in general are pressurized.
My question is specifically about the A330-243F in the below photograph. That looks like a pressure withstanding door/bulkhead dividing the fore crew compartment from the aft cargo compartment. Is that correct, and does it mean the aft cargo compartment is not pressurized? It's also possible both are pressurized and it's an airtight door for fire/fumes control.

Source
As mentioned in the linked question, it's likely both compartments are pressurized because of the efficient shape of the pressure vessel and so that the same pressurization system can be used across both passenger and cargo variants.

You're correct- for cargo aircraft derived from passenger planes, the cabin is pressurized. This reduces the complexity and certification requirements. Also, this allows for easy conversion too. The thick door may be due to two reasons:

To improve load carrying/transferring capacity- airbus talks about

... the aircraft’s reinforced fuselage and doors, which increase shear and bending/running loads..

also, the thick door will help protecting the crew should the cargo move forward in flight.
To act like an airtight seal between the cabin and cockpit, so that it prevents smoke ingress into cockpit and to enable the crew to extinguish fire. FAA Class E (for cargo aircraft) requires isoaltion between the cargo compartment and cockpit.

Another thing to note is that even a number of military 'cargo' aircraft have pressurized cabins (An-124, I think is among  exceptions), as they are also used in Medivac and causality evacuation roles- these require the cabin pressure to be set higher than normal.

I'm guessing Airbus is talking about doors in the fuselage, not inside the cabin.

A primary reason military transports are pressurized is to get them above the range of small arms and light AA weapons. Also, the greater speed and range that an aircraft has when flying at higher altitudes.

Also, extinguishing main-deck fires on cargo aircraft generally involves depressurising the cabin, requiring the cockpit bulkhead to withstand a full pressure differential.

The wall is a rigid barrier behind the supernumerary section that serves two purposes.
The first purpose is protect the supernumerary area and cockpit from cargo shifting forward during an accident. The barriers are rated to be able to hold back a full load of cargo at crash loads (9G*). This allows for the primary cargo securing system to only have to handle flight loads, making it lighter and less bulky, meaning more cargo can be carried.
The second purpose is to act as a smoke and air barrier. If a fire is detected in the cargo area, airflow to the compartment is shutoff. The rigid barrier then prevents smoke from crossing into the supernumerary/cockpit and keeps fresh air from crossing into the cargo area. Loss of fresh air should lead to the fire extinguishing, some aircraft will also depressurize the aircraft to extinguish a main deck fire. See 14 CFR 25.857 Paragraph (e).(4)-(5) (note that main deck cargo is a Class E cargo compartment).
The door is used to allow access to the cargo area during loading and during flight for various reasons. The door is not pressure rated.
*The crash landing loading of 9G is defined by 14 CFR 25.561. Although the FARs do not directly mandate that the barrier be used as crash barrier, it does mandate that the cargo subjected to 9G would not injure crew or block their egress path. Using a rigid barrier to react the crash loads is a design decision made to optimize cargo capacity.

@ymb1 I added the FAR references to the post. Hope this helps.

In the good old days there was no wall, instead there was a net which was designed to prevent any loose load from coming into the galley/supernumerary seating area (commonly referred to as a G-net. There was also a smoke barrier which was affixed by velcro to the prevent any smoke from entering the aforementioned area.
Even the 747 combis had the net and smoke screen. The aft wall had no load restraint capabilities and apart from making things look nice it served as a form of insulation against cold and noise.
The net was not ideal as it could not prevent the movement of sharp/pointed objects as the lattice of the net was quite big, around 8-10 inches IIRC. So if you had a load of pipes or bars you had to have x number of compressible load ULDs (cargo which was of a certain density) which would act as the barrier to prevent the pipes/bars from going thru the g-net and into the galley/supernumerary seating area.
Certification requirements changed and I believe it is now mandatory for new build/newly converted to cargo aircraft to have a fixed bulkhead. This is not so much a pressurisation issue but more to prevent smoke and cargo from entering the galley/cockpit.


text:
What airplane does this vintage instrument panel come from?

Can anyone please tell me what this is from?
It looks like it's military. I have a few panels that came with this and gauges (not if it's a b-16)

Does looking up the N-number on the panel help at all?

@UnrecognizedFallingObject I searched, the FAA says it is not registered.

@Federico -- hrm.  I wonder if there's some historical registrations archive out there?

i think you might of got it i looked up cirrus glider it looks similar t\

What makes you say it's "vintage"?

Any info on how this panel made it all the way to Canada (possibly donated to an aviation museum in Brandon MB) and then passed along to me. Seems like it has had an interesting history.

The shape makes it clear that this is from a single seater or tandem aircraft. This makes a glider very likely, which is supported by the "Vario" engraving over the column of small holes on the bottom right.
A little googling then brings me to this page and the assumption that this panel is from a Schempp-Hirth Standard Cirrus, Serial No. 176. The plane was badly damaged at Minisink, NY on October 23, 1976 in a botched landing and consequently written off. At that time it was registered as N11JY.

Schempp-Hirth Standard Cirrus (picture source)

Standard Cirrus instrument panel (picture source)

ok great thank you so much for your help

Misread "Minisink" as "Minsk" and was wondering what on earth a US-registered glider was doing in the Byelorussian SSR...

It has the legend "Vario", short for variometer stenciled on it and it looks very much like the panel from a Cirrus sailplane.

Source.  Standard Cirrus


text:
Would the twin engine Boeing Y3 be able to compete better than the Airbus A380?
The low sales performance of the quad engine Airbus A380 and declining sales of the Boeing 747-800 have largely been attributed to lesser fuel economy of quad engine aircraft when compared to their newer more fuel efficient twin engine counterparts.
The image rendering of the future Boeing Y3 aircraft shows a jumbo size twin engine twin deck aircraft the size of an Airbus A380.
Whether or not a prototype was ever made, in light of fuel economy technology improvements more prevalent and effective in twin engine configurations like the GE9X, would the twin engine Boeing Y3 be able to compete better than the quad Super jumbos and Jumbo respectively the Airbus A380 and the Boeing 747-8?

I think you should re-word your question, if not rework it completely. As it stands it calls for opinions and hypothesis, something that here is considered off-topic.

Edited to add the words: The low sales performance of the quad engine Airbus A380 and declining sales of the boeing 747-800 have largely been attributed to lesser fuel economy of quad engine airgcraft whne compared to their newer more fuel effiient twin engine counterparts.

The low sales performance of the A380 has got very little to do with the (specific) fuel consumption of their engines, or the number of engines. It's because it has too many seats, and most airlines can't fill it, and then the cost per seat mile is uncompetitive. Emirates operate it with 615 pax, in comparison the Boeing 777-10X is planned for 450. Not many routes have enough demand to fill such a large plane. See "Airlines are abandoning the world's biggest passenger plane." https://qz.com/782361/airbus-a380-airlines-are-abandoning-the-worlds-biggest-passenger-plane/

As said by others, please do not add images that do not help understand the question. And moreover, if you really need to add an image, at least provide the source of said image.

The answer is quite simply, no, at least, not if it is or was intended to compete as an airliner of roughly the same size.
That's because your question is based on a false premise, that the struggles of the A380 in the current market are due to its fuel economy.
The A380 is indeed uneconomic to operate except on few routes, but that is because of its size and capacity - which on most routes, can't be filled.
The market has changed since the A380 was conceived and launched; airlines are using more and smaller aircraft with more connections, between more minor airports.
To a lesser extent, new regulation has made a difference too. It has allowed smaller aircraft with twin engines - which are more flexible in an airline's operations - to take on routes that previously were considered suitable only for four-engined aeroplanes.
The technology and fuel consumption of the A380 are perfectly adequate to serve for decades into the future. It has been overtaken not by technological advances in its rivals, but by forces that change much faster than technology can: market conditions, and regulation.
Aircraft that will be selected instead of the A380 by airlines won't be chosen because they have better fuel economy (and even less so, marginally better fuel economy because they have two engines rather than four) but because they fit market needs better.

Regulations should NEVER interfere with the free functioning of markets unless its relaxing previously stringent regulations that were affecting free functioning of markets, because if they do, they are costing the industry billions in losses and billions in lost revenue.  That said Decision makers at Airbus should have taken into account that regulations that gave them an unfair advantage before authorising the billions and time spent in the design and manufacture of the Airbus A380 may change and hence prevented losses

thanks for the answer.  by the way and may I know which regulations changed and how the affected the Airbus A380?

@securitydude5 Are you serious? What do you imagine the safety record of aviation would be were it not for stringent regulation? But to answer your question in the next comment, the most obvious changes in regulation that affected the A380 would be changes to ETOPS. ETOPS-240 was introduced shortly after the A380's launch; since then twins have been certified for ETOPS-330 and ETOPS-370. The advantages of four engines have steadily diminished. I've no idea what you might mean by "regulations that gave an unfair advantage".